Irrigation Water Quality-76



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Project Leader and Principal UC Investigators

Glenn Nader, livestock farm advisor, UC Cooperative Extension Butte/Sutter/Yuba Counties


Definite federal and state water-quality objectives are now being established.

Because rice production uses public waters and drainage systems, it is essential to develop research information on the quality of the water as received and later returned to drainways. The Board has supported such research since 1969.

In 1974, a major study was conducted in fourteen commercial rice fields selected to represent typical rice-producing areas in the Sacramento and lower San Joaquin valleys. Surface outflow from commercial fields in general was shown to differ little from inflow in all quality aspects tested. Individual comparisons vary and in some cases the outflow value was more favorable than the inflow.

It has not been possible to evaluate the quality of percolating water on the basis of subsoil water samples. The subsoil salts in some fields have not been leached out despite several years of flooding for rice, indicating that almost no water is percolating through. Only where percolation or seepage is relatively rapid can the subsoil water composition be considered representative of the underground outflow.

Public Law 92-500 and the NPDES permit system will affect all irrigated agriculture, including rice production.

The discharge of wastewaters into navigable waters is regulated by PL 92-500, the 1972 Federal Water Pollution Control Act. Under the National Pollutant Discharge Elimination System (NPDES), a permit is required for "point-source" (collected) discharges of pollutants (salts, nutrients, pesticide residues, sediments). Public Law 92-500 is intended to eliminate by 1985 the discharge of pollutants into U.S. waters, with an interim goal of achieving by 1983 water quality that is "fishable and swimmable." Uniform waste-discharge requirements are being promulgated. All irrigated agriculture is required to apply for an NPDES permit and self-monitor its surface irrigation return flows in terms of quantity and quality of flow. It was contemplated that this information and data on agricultural drainage would be used to develop uniform waste discharge requirements similar to those for municipal and industrial discharges. At first glance, irrigation tailwater management appears to be a logicial and practical control technology. If tailwater is controlled and/or reused, irrigation application efficiency would be improved, water conserved, and energy also in some situations. In theory, then, water-quality problems might be substantially reduced. This working premise will need proof, however.

Some preliminary conclusions and recommendations with regard to PL 92-500.

Parallels cannot easily be drawn between industry and agriculture. Irrigated agriculture does not utilize "plumbing and valves" found in most industrial sites, and it operates on an "open system" utilizing available natural resources and conditions which are difficult to manage. The pertinent facts are:

  1. If irrigated agriculture is to comply with the intent of PL 92-500, it will require controls and policies that are reasonable, flexible, attainable, and different from those of most other industries.
  2. Rather than concentrating on "end-of-pipe" controls, due consideration should be given to performance standards.
  3. It is difficult to recommend any single universal management practice, since control technology may vary from one location to the next. Furthermore, the effect(s) of tail-water discharge may be beneficial, detrimental, or both, depending on the quality constituents of interest and the water-flow regime.
  4. In the management of water quantity and quality, proposed plans should evaluate "controllable" return flows and waste loads as to effectiveness separately from those that are "uncontrollable or difficult to control." Other effects need to be considered as well, such as the potential danger of transferring a pollution problem from surface to groundwater bodies.
  5. Individual site factors and conditions should be considered in developing controls and standards which are compatible with state and national goals and mutually beneficial at the interbasin levels.
  6. The self-monitoring period of point discharge of return flows should encompass the irrigation season, including any lag time between cessation of irrigaton and discharge. In many areas, year-round monitoring would be desirable.


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